The liquid crystal display devices using the liquid crystalline compound (in this description, the term of a liquid crystalline compound is used as a generic term for a compound exhibiting a liquid crystal phase or a compound not exhibiting a liquid crystal phase but useful as a constituent of a liquid crystal composition) are broadly used in displays of clocks, watches, electronic calculators, word processors and the like.
Lately, much research has been conducted for a TFT type display having properties such as a high contrast and a wide viewing angle. Liquid crystal compositions for TFT need physical properties, such as a high voltage holding ratio, low threshold voltage (Vth), little variation of these properties depending on temperature, broad temperature range of liquid crystal phase and low viscosity. Further, the compositions having a high optical anisotropy (.DELTA.n) are useful for improving the response speed.
For these reasons, compounds of fluorine types are preferably used, as described in (1) Japanese Patent Publication 63-13411, (2) Japanese Patent Publication 63-44132, (3) Japanese Patent Laid-open 2-233626, (4) Japanese Patent Laid-open 2-501311, (5) Japanese Patent Laid-open 3-500413 and (6) DE4301700, many synthesis methods and researches have been done.